1. Field of the Invention
The present invention relates to a copolymer resin composition, a molded product, and a method of manufacturing a copolymer resin composition.
2. Description of the Related Art
Due to the raising of awareness of a recent global warming issue, technical development for providing biodegradability and reducing an amount of a used fossil resource has been actively conducted. One of these developments is a movement to replace a plastic material whose raw material is petroleum with a biomass material.
Meanwhile, many resin components are utilized for components used in an electro-photographic instrument such as a copying machine or a laser printer or an image output instrument using an ink jet technique or components of an electric or electronic instrument such as a home electric appliance or interior equipment of an automobile. These resin components are almost all made of a raw material of petroleum but an alternative technique for a biomass resource-derived resin is desired in view of an issue of reduction of an amount of emitted carbon dioxide, an issue of depletion of a petroleum resource, an issue of a non-biodegradable plastic, and the like.
A biomass resource means a resource of a product from an organism such as a plant or an animal, and indicates not only a conventionally known raw material such as wood, cotton, silk, wool, or a natural rubber but also starch obtained from corn, a soy bean, or an animal, a fat and oil, raw garbage, or the like. A biomass resource-derived resin is made from a raw material that is such a biomass resource, and generally, is often a biodegradable resin. A biodegradable resin is a resin which is decomposed by a microbe(s) at a condition of temperature and humidity under a natural environment. Additionally, a biodegradable resin is not only a biomass resource-derived resin but also may be a petroleum-derived resin, however, most of petroleum-derived resins are non-biodegradable. For a biomass resource-derived biodegradable resin, there is known a polylactic acid (PLA) made by chemical polymerization of a lactic acid as a raw material which is provided by fermenting a carbohydrate such as potato, sugar cane or corn, an esterified starch based on a starch, a polyhydroxy alkanoate (PHA) which is a microbe-yielded polyester resin that is yielded inside the body of a microbe, a polytrimethylene terephthalate (PTT) whose raw materials are 1,3-propanediol obtained by a fermentation method and terephthalic acid derived from a petroleum, or the like.
Furthermore, while a PBS (polybutylene succinate) whose raw materials are butanediol and succinic acid is manufactured from petroleum-derived raw materials at present, a study for transferring to a biomass-derived resin is being conducted, and manufacturing of succinic acid as one of principal raw materials from a plant in the future is being studied.
Among the biomass resource-derived resins, a polylactic acid has a melting point around 180° C. which is high, is comparatively excellent in a moldability and processability thereof, and is supplied to the market in a stable amount thereof, and a molded product to which it has been applied has been put in practical use. However, a polylactic acid has a glass transition point around 56° C. which is low, and accordingly, has a drawback of a heat distortion temperature around 55° C. which provides a low heat resistance. Furthermore, a polylactic acid is a crystalline resin, and accordingly, has a low impact resistance, wherein an Izod impact strength thereof is 2 kJ/m2 or less, whereby it is difficult to conduct employment thereof for a durable member of a product of electric or electronic instrument.
It is known that one way to improve a physical property of a polylactic acid is a method for making a polymer alloy together with a polycarbonate resin which is a petroleum-derived resin. However, the rate of a used petroleum-derived resin is high in order to ensure a physical property of a molded product and the rate of an included biomass resource-derived resin is only able to be around 50% whereby the effect of reducing an amount of emitted carbon dioxide or the effect of reducing an amount of a used petroleum for reduction of an environmental load is reduced by about half.
Meanwhile, a polylactic acid is a crystalline resin, and hence, a technique for facilitating crystallization thereof to improve the heat resistance thereof has been studied. For a crystallization method, there are known a method of reheating (annealing) after molding to improve a degree of crystallization and a method of molding while a crystallization nucleating agent is added. A method of annealing after molding does not only have problems of a complicated molding process and a long time period of molding but also is required to provide a die for annealing or the like in order to avoid deformation involved with crystallization, and thus there are problems in the cost and productivity.
For a method of adding a crystallization nucleating agent, development of a crystallization nucleating agent to improve a degree of crystallization and a rate of crystallization is advanced, but, even if a crystallization nucleating agent is added, a time period of crystallization of about 2 minutes is required at present, and accordingly, it is not possible to conduct molding in a time period of a molding cycle similar to that of a petroleum-derived and general-purpose resin. Furthermore, it is necessary to conduct crystallization at a temperature around 100 to 110 degrees, whereby it is not possible to conduct molding by using an inexpensive water cooling-type die temperature control machine and there is a problem of increasing of an environmental load due to a required high temperature. Moreover, when only a polylactic acid is crystallized, a deflection temperature thereof under load is around 55° C. at a high load (a load of 1.80 MPa) even if sufficient crystallization is conducted by annealing or the like, whereby there is a problem of an insufficient heat resistance.
A microbe-yielded polyhydroxy alkanoate (PHA) resin that is excellent in a heat resistance thereof is easy to cause thermal decomposition at the time of heating and there is a problem of a physical property degradation caused by thermal decomposition when a molded product is produced by a processing method such as injection molding. It is difficult to suppress reduction of a molecular weight of a polyhydroxy alkanoate resin even if a conventional thermal stabilizer, an antioxidant, or an anti-hydrolyzing agent is added thereto.
Specific documents in regard to manufacturing of a biodegradable resin from a biomass resource-derived resin will be provided below.
Japanese Patent Application Publication No. 2006-335909 and Japanese Patent Application Publication No. 2007-056247 propose methods of blending of about half of a resin whose raw material is a petroleum resource, such as a polycarbonate resin, into a polylactic acid resin to improve a deflection temperature under load or an impact resistance. For example, Japanese Patent Application Publication No. 2006-335909 discloses a component for an electronic instrument characterized by including 20-80 parts by mass of a polylactic acid, 20-70 parts by mass of a polycarbonate, and further 0.1-50 parts by mass of a reinforcing material, and 0.5-35 parts by mass of a flame retardant. Furthermore, Japanese Patent Application Publication No. 2007-056247 discloses a resin composition provided by compounding 0.1-50 parts by weight of a flame retardant to a polymer compound of 95-5% by weight of a polylactic acid resin and 5-95% by weight of an aromatic polycarbonate resin, which polymer compound is graft-polymerized with 0.1-50 parts by weight of an acryl resin unit or styrene resin unit, relative to the total amount of those resins of the polymer compound as 100 parts by weight.
Furthermore, as described in Japanese Patent Application Publication No. 2007-231034 and Japanese Patent Application Publication No. 2005-023260, a biomass-type filler material such as a paper powder, a wood powder or a natural fiber is added into a polylactic acid resin whereby it is possible to improve the mechanical strength of the resin. By using this method, it is possible to improve the rate of a constituting biomass material without using a petroleum-derived resin. For example, Japanese Patent Application Publication No. 2007-231034 proposes a material for a housing characterized by mixing and kneading a natural fiber impregnated with a flame retardant with at least a plant resource-derived resin, wherein a fiber selected from the group composed of kenaf fibers, hemp fibers, and jute fibers is disclosed for the natural fiber.
Japanese Patent Application Publication No. 2005-023260 proposes an electric or electronic component provided by molding a resin composition which is provided by compounding 1-350 parts by weight of a natural product-derived organic filler material relative to 100 parts by weight of a plant resource-derived resin. It is characterized that the plant resource-derived resin is a polylactic acid resin and the natural product-derived organic filler material is at least one kind selected from paper powders and wood powders wherein 50% by weight or more of the paper powder is a waste paper powder. Furthermore, it describes that a crystallization nucleating agent is added in order to improve the heat resistance of a polylactic acid resin or a plasticizer as a crystallization facilitating agent is added whereby it is possible to improve a degree of crystallization of a polylactic acid resin.
Japanese Patent Application Publication No. 2007-077232 proposes a biodegradable polyester-type resin composition for accelerating a crystallization rate of an aliphatic polyester-type polymer (P3HA) composed of a repeating unit represented by a formula of [—CHR—CH2—CO—O—] (in which formula, R is an alkyl group represented by CnH2n+1 and n=an integer of 1 or more and 15 or less) whose crystallization is particularly slow among biodegradable polyesters and for improving a processability and a processing rate in a molding process such as injection molding, film molding, blow molding, fiber spinning, extrusion foaming, bead foaming, or the like. Such a biodegradable polyester-type resin composition is a mixture of a P3HA yielded from a microbe and a crystallization nucleating agent composed of one or more kinds selected from polyvinyl alcohols (PVAs), chitins, and chitosans, wherein it is considered that PVAs, chitins, and chitosans are suitable crystallization nucleating agents for a P3HA. Additionally, a poly(3-hydroxybutyrate (P3HB) and a copolymer of (3-hydroxybutyrate (3HB))/(3-hydroxyhexanoate (3HHx)) are disclosed for a specific aliphatic polyester-type polymer.
Japanese Patent Application Publication No. 2006-274182 proposes a polylactic acid resin composition for optics which is composed of a polylactic acid-type resin, a polyhydroxyalkanoate copolymer, and a carbodiimide compound. Such a polylactic acid resin composition for optics is excellent in a transparency, has an improved tensile characteristic, and contains 99.9-80 parts by mass of a polylactic acid resin and 0.1-20 parts by mass of a polyhydroxyalkanoate copolymer.
Japanese Patent No. 3609543 proposes an aliphatic polyester-type polymer blend including a lactic acid-type polymer and a hydroxyalkanoic acid-type polymer, which is intended to increase the biodegradability of a lactic acid-type polymer that is a biodegradable resin and improve a moldability thereof. It is considered that such an aliphatic polyester-type polymer blend has a high biodegradability and an improved moldability and further is excellent in a characteristic of a molded product.
Japanese Patent No. 3599533 proposes a heat-resistant resin composition which contains a polylactic acid and an aliphatic polyester other than polylactic acids and includes a crystalline SiO2 as a crystalline inorganic filler component. Such a heat-resistant resin composition includes (A) a polymer composition component which contains (a1) 75-25% by weight of a polylactic acid and (a2) 25-75% by weight of an aliphatic polyester with a melting point of 100-250° C. other than polylactic acids and (B) 0.1-70 parts by weight of a crystalline inorganic filler component which contains 10% by weight or more of a crystalline SiO2 relative to 100 parts by weight of the polymer composition component (A). It is considered that such a heat-resistant resin composition is capable of being injection-molded at a die temperature that is a glass transition temperature (Tg) or lower or around room temperature (0-60° C.), has a high crystallization rate and a sufficiently high degree of crystallization in a molding process, thus accordingly has an excellent heat resistance, is difficult to cause degradation of a polymer component in use, and has a property for hardly causing embrittlement. In a specific and practical example, a resin for which a polybutylene succinate has been used is disclosed, and a chemical polymerization treatment method such as a dehydration or condensation polymerization method, an indirect polymerization method for melting and polymerizing a cyclic dimmer, a ring-opening polymerization method for melting and polymerizing a cyclic dimmer under the presence of a catalyst, or the like, is illustrated for a method of manufacturing an aliphatic polyester.
International publication No. 02/006400 proposes a lactic acid-type resin composition composed of a mixture of (A) a mixture of (a1) a polylactic acid and (a2) an aliphatic polyester and (B) an aliphatic block copolyester having a polylactic acid segment and an aliphatic polyester segment. Such a lactic acid-type resin composition is excellent in a moldability, a flexibility and a safety and further has a biodegradability after use whereby waste disposal is facilitated. In such a lactic acid-type resin composition, an aliphatic polyester(s) (a2) is/are a polybutylene succinate and/or a polycaprolactone and 2-component mixture (A) composed of a polylactic acid (a1) and an aliphatic polyester (a2) is compatibilized with a 2-component aliphatic block copolyester (B).
Even if a petroleum resource-derived resin such as a polycarbonate resin is blended with a polylactic acid resin by about half to improve a heat resistance or a mechanical strength, the effect of replacing a resin product with a biomass material is only reduced by half from the viewpoint of a countermeasure for global environment. Furthermore, the price of a petroleum-derived resin used for a blend may be elevated depending on a tendency of depletion of crude oil in the future so that it may be impossible to use a petroleum-derived resin substantially.
When a method is used which utilizes a natural organic substance-type filler material such as a paper powder, a wood powder or a natural fiber for a polylactic acid resin, it is possible to increase the ratio of a constituting biomass material to provide a resin composition for which a petroleum resource is hardly used. However, for example, the particle size of a paper powder, a wood powder, or a natural fiber used in Japanese Patent Application Publication No. 2005-023260 is about 1-10 mm, whereby the paper powder, the wood powder, the natural fiber, or the like emerges on the surface of a resin component, and hence, is not able to be used for a molded product requiring a high appearance precision or beautiful appearance, such as an exterior housing of an electric product. Furthermore, when a paper powder, a wood powder, or a natural powder is pulverized in order to improve an appearance precision or beautiful appearance, an increase of a production cost is caused.
While it is necessary to increase a degree of crystallization in order to improve the heat resistance of a polylactic acid resin, a method of adding a crystallization nucleating agent or adding a plasticizer as a crystallization promoter is known for increasing a degree of crystallization. However, it is known that even if the degree of crystallization of a polylactic acid resin is thus increased, a deflection temperature under load is merely improved to about 55° C. at a high load (for example, 1.80 MPa). Furthermore, a high die temperature and a long molding time period are required for crystallizing a polylactic acid, and, for example, a die temperature of 100° C. and a molding cycle time period of 90-100 seconds are needed for molding a tensile test piece with a thickness of 3 mm. For a conventional fossil resource-derived resin (for example, a polypropylene or a polystyrene), a molding cycle time period for molding a similar tensile test piece is no more than about 30 seconds at a die temperature of about 50° C., and a large problem in industrial production of a molded product of a polylactic acid resin is as to a facility of molding.
On the other hand, utilization of a biodegradable resin whose monomer unit is 3-hydroxybutyric acid (3HB) or 3-hydroxyvaleric acid (3HV) has been considered for a polyalkanoate resin containing no lactic acid. Among these, a copolymer of 3-hydroxybutyric acid-3-hydroxyvarelic acid is able to be yielded by means of microbe fermentation on a glucose-based medium and is expected to be an alternative item of a polylactic acid resin or a complementary resin for a blend or the like. However, a 3HB-3HV copolymer is readily thermally-decomposed and there is a problem of degradation of a physical property due to decomposition at a step of a molding process such as injection molding. It is not possible to solve such a problem by increase of the molecular weight of a copolymer, addition of a crystallization nucleating agent, or blending of a polylactic acid resin.
In regard to a biodegradable polyester-type resin composition as described in Japanese Patent Application Publication No. 2007-077232, a crystallization temperature of a specifically disclosed biodegradable polyester-type resin composition to be molded is 110° C. which is high (see FIG. 4 in Japanese Patent Application Publication No. 2007-077232) and it is difficult to control a die temperature to about 90° C. or lower which is the upper limit of the temperature of a water-cooling-type temperature control machine. Furthermore, an amorphous portion remains even for a molding time period of 40 seconds, and accordingly, it is considered that it is difficult for crystallization to proceed sufficiently. Moreover, a polyhydroxybutyrate or a polyhydroxybutyrate-hydroxyvalerate copolymer has a problem of a significant reduction of a molecular weight in a thermal process which causes reduction of the strength of a resin molded product or the like.
A polylactic acid resin composition as disclosed in Japanese Patent Application Publication No. 2006-274182 is a transparent material for optics and is not crystallized but solidified at an amorphous state, and hence, it is considered that a heat resistance is not sufficient in order to be used for a housing of an electric or electronic instrument or the like. As guessing from a disclosed configuration, the heat resistance of such a polylactic acid resin composition is supposed to be about 55° C.-60° C. which is around a glass transition point of a polylactic acid.
A specific configuration of an aliphatic polyester-type polymer blend as disclosed in Japanese Patent No. 3609543 is a polymer blend of an aliphatic polyester containing a polyethylene glycol chain in the main chain thereof and a poly(3-hydroxybutyric acid) (P3HB). However, no crystallization nucleating agent is included, and hence, it is considered that there remain problems of improvement of a heat resistance, lowering of a molding temperature, and a reduction of a molding time period.
For a heat-resistant resin composition as proposed in Japanese Patent No. 3599533, further improvement of a heat resistance is desired. Furthermore, a study of a method for manufacturing a resin which is not based on a chemical treatment in polymerization but based on a microbe treatment is expected.
For a lactic acid-type resin composition as proposed in International Publication No. 02/006400, an aliphatic block copolyester (B) having a polylactic acid segment and an aliphatic polyester segment is used to improve the compatibility between a polylactic acid (a1) and an aliphatic polyester (a2) in a mixture (A) thereof. Hence, it is necessary to specially select the composition or molecular structure of an aliphatic block copolyester (B).
As described above, a general-purpose resin having a biodegradability and being producible economically for which it is possible to use a biomass raw material is still being developed. In particular, no resin composition having a heat resistance over 60° C. which could not have been achieved by a polylactic acid, being excellent in a moldability and is capable of being used for a general-purpose molded product has been obtained. Most of biomass-type resin compositions which are considered to be capable of being used practically are intended to blend a petroleum-type resin into a polylactic acid so as to improve the property thereof and a process for kneading a resin is required. Furthermore, many of biomass-derived polyester resins have less favorable thermal decomposition characteristics and the problem is that when a shear stress is applied at a high temperature for a long time period in a process of kneading two or more kinds of resins, degradation of a physical property occurs readily. Moreover, a blending technique for stabilizing a physical property is needed for a resin blend, in view of a change in the compatibility of each of the resins, the difference between crystallization temperatures thereof, or the like.